Styrene-butadiene copolymer resins (hereinafter, also referred to as “SBC resin”) are known to have high flexibility due to a butadiene rubber component contained therein and in addition have excellent transparency and processability, and by virtue of the feature, they have been conventionally used for a wide variety of applications such as packaging materials for food, packaging materials for electronic parts, blister packages, and toys.
Although the SBC resin may be used singly in these applications, it is more common that an SBC resin is used in a blend with a styrene homopolymer resin (GPPS), a polystyrene resin such as an high impact polystyrene (HIPS), or a styrene-alkyl (meth)acrylate copolymer resin.
The reason is, for example, that such blending facilitates control of balance between impact resistance and stiffness and balance between mechanical characteristics and economic efficiency in the material design. Specifically, use of two starting materials of an SBC resin and a polystyrene resin with the blending ratio between them adjusted provides the intended properties of a product, and moreover a wide variety of materials can be produced in accordance with the intended properties of a product.
Many techniques have been previously disclosed in which an SBC resin having a high copolymerization ratio of styrene and a styrene-butadiene copolymer elastomer (hereinafter, also referred to as “SBS elastomer”) having a low copolymerization ratio of styrene and being excellent in flexibility are combined and blended with a polystyrene resin or styrene-alkyl (meth)acrylate copolymer resin to obtain a resin composition being transparent and excellent in flexibility and impact resistance.
For example, Patent Literature 1 discloses a polystyrene resin composition comprising an SBC resin, an SBS elastomer, and a polystyrene resin.